The present invention relates generally to automatic windshield wiper control systems wherein the windshield wipers of a motor vehicle are activated in response to sensed precipitation and, more particularly to such a windshield wiper control system including an improved precipitation sensing element.
A variety of automatic control systems are known for activating the windshield wipers of a motor vehicle in response to sensed precipitation. These systems utilize various types of precipitation sensors which include, for example, a microwave sensing system as disclosed in U.S. Pat. No. 3,786,330. More conventional precipitation sensors typically include pairs of parallel or interleaved electrical conductors which are formed onto substantially planar surfaces.
These more conventional detectors often form a portion of the windshield of a motor vehicle or are connected to the windshield such that they can be "cleared", i.e., returned to a nonprecipitation indicating state, by means of the wiper blades of the windshield wiper system or an auxiliary wiping device activated thereby. See, for example, U.S. Pat. Nos. 1,482,448; 2,407,215; and 3,555,289.
Alternatively, the precipitation sensing elements are cleared by heating as disclosed in U.S. Pat. No. 4,317,073 or by means of centrifugal force as disclosed in U.S. Pat. No. 3,649,898.
Self-clearing precipitation sensors are known in the art, for example, as disclosed in U.S. Pat. Nos. 2,823,346 and 4,010,383. However, known self-clearing precipitation sensors are difficult to construct requiring a series of closely interwoven wires in the former patent and precision formed and placed comb-like sensor elements in the latter patent. It is thus apparent that the need exists for a self-clearing precipitation sensing element which is easily constructed and, hence, inexpensive.